Process for the separation of gamma benzene hexachloride



Nov. 3, 1959 B. H. NICOLAISEN ETAL 2,911,446

PROCESS F OR THE SEPARATION OF GAMMA BENZENE HEXOCHLORIDE Filed July 7,1953 2 Sheets-Sheet 1 CRUDE 514C? h REG a6 l0 fxrfiAcr/A/swwr/o/v ERACTOR FRESH W451; 50L VEN T? 5EPARATOR 8 WASH/ED ALPHA, CRYSTALUZER //3BETA 01x5 //l/ I E S/JWASH SEPARArOR SOLVE/VT) 1 /2 WASHED GAMMA W45Saws/v1 C'A/(E ST/LL F/LTRATE ZRES/DUE ma a v ATTORNEYS Nov. 3, 1959 AB. H. NICOLAIISEN ETAL 2,911,446

PROCESS FOR THE SEPARATION OF GAMMA BENZENE HEXOCHLORIDE Filed July '7,1953 2 Sheets-Sheet 2' Etta a5 l0 fXTR/lCT/NG -50LUT/0N? EXTRAU'OH{FRESH 1 1445 50L VEN r 5EPAPA 70R &

W4 SHE'D ALPHA, 30A? 6 E BETA CA K5 TANK 2/3 O-PKSTA LL/Z ER FRESH WASH5594 RA TOR & 5 SOLVE/VT J 1' WASHED GAMMA SURGE WASH SOLVE/VT C A K ETANK .5 TILL /L TRATE 1 R55 mug INVENTORS BERNARD H. M00; A/SEN Juoso/vA- l ,l OOD ATTORNEYS large scale.

United States Patent O F PROCESS FOR THE SEPARATION or GAMMA BENZENEHEXACHLORIDE Bernard Nicolaisen, Kenmore, and Judson A. Wood,

Niagara Falls, N .Y., assignors to Olin Mathieson Chemical Corporation,a corporationof Virginia Application July 7, 1953, Serial No. 366,602

4 Claims. (Cl. 260- 648) This invention relates to the production ofgamma benzene hexachloride by separation of concentrates containing 95%or more of the 'gamma isomer of benzene hexachloride or1,2,3,4,5,6-hexachlorocyclohexane from crude benzene hexachloride bymeans of solvent extraction.

Benzene hexachloride as usually manufactured by the additionchlorination of benzene contains about 10-15% of the gamma isomer,60-80% alpha isomer, 10% beta isomer and small percentages of otherbenzene hexachloride isomers together with a few percent ofheptachlorocyclohexane and other byproducts. The gamma isomer of benzenehexachloride is the only one of these products having significantinsecticidal activity. Although the crude mixture may be used forinsecticidal purposes, it is advantageous to separate concentrates ofthe gamma isomer which contain larger proportions of the insecticidallyactive isomer. I

The various isomers of benzene hexachloride may be separated by variouscombinations of extraction, crystallization, distillation and otherprocesses. Many of the processes that have been proposed are noteconomically feasible or are ineffective. In order to obtain gammaconcentrates at the lowest possible cost, the. number of steps,especially distillations and mechanical losses, must bekept to aminimum. Furthermore to be economically advantageous, a process mustseparate substantially all of the gamma isomer from the crude benzenehexachloride. Processes in which partially separated materials tend toaccumulate cannot be used economically on a large or a continuous scale.The present invention provides a process for treating crude benzenehexachloride to recover substantially all of the gamma isomer containedtherein as concentrates containing 95% or more of the gamma isomer.

Many of the known processes require long periods of extraction orcrystallization approximating 48 hours. This necessitates largeequipment when operated on a The present invention provides a process inwhich no holding times greater than about 4 hours are required and isthus amenable to continuous operation.

Although the separation of the alpha and beta isomers from the gammaisomer of benzene hexachloride is rela are obtained: an essentiallygamma-free cake and a washed gamma cake. All of the isomers except.gamma and all of the by-product heptachlorocyclohexane are rejected inthe first cake. The process requires only one extraction step and onecrystallization step, each followed by a suitable step of separation ofproducts. A solvent recovery still is also provided. Only onedistillation of wash solvent is necessary per cycle and make-up solventrequirements are very low. No unseparated, gammacontaining residues areproduced except the small amount of residue from distillation of thewash liquor. This is recycled and represents but a small proportion ofthe crude charged.

The invention utilizes the fact that a solution saturated with respectto any of the isomers at a given temperature will not extract furtherquantities of that isomer from a crude solid containing it incrystalline form. It further utilizes the fact that gamma benzenehexachloride crystallizes more readily than any of the other isomersfrom a solution of mixed isomers in any of the various suitablesolvents. The other isomers have a greater tendency to remain insupersaturated solution than gamma.

The process of this invention is characterized by cyclic operation inwhich solution is circulated in a closed cycle between an extractionstage and a crystallization stage. Thus the crude solid is extractedwith a solution saturated with respect to all of the isomers exceptgamma. Only gamma is extracted from the solid and goes. into solution.On cooling slightly, due to the higher crystallization tendency of gammaand the higher supersaturation tendency of the coproducts, the extractdeposits crystals of pure gamma isomer, leaving the co-products insupersaturated solution. On warming the filtrate to the extractiontemperature, the solution is saturated with respect to all isomersexcept gammaiand is againcapable of extracting that isomer only from thecrude benzene hexachloride. v It is recycled as the extracting solventfor treatment of additional crude benzene hexachloride. An organicsolvent, e.g. perchlorethylene, for benzene hexae chloride, havingdifferential aflinity for the isomers of benzene hexachloride at leastwith respect to'solutiom rates is employed as the extraction andcrystallization medium. Fresh solvent is used only to wash theundissolved solids remaining after the extraction step and to wash thepure gamma cake. These washings are combined and distilled to recoversolvent. The minor proportions of benzene hexachloride dissolved in thewashing operation remain as a residue which may be recycled to theextractor.

It is advantageous to Waslr'the cakes with water containing a smallamount of a wetting agent to displace any liquor from the crystals. Forthis purpose, about 0.1% to about 5% of wetting agent may be used. Thelatter may be of the cationic type, for example, long chain quaternaryammonium salts such as lauryl pyridinium chloride, of the anionic type,for example, sulfonates or sulfates such as sodium kerylbenzenesulfonateor sodium lauryl sulfate, or agents of the non-ionic type, for examplethe phenoxypolyoxyethylene ethariols. These washings may be discarded.The liquor may be separated and returned to the process.

Figures 1 and 2 of the accompanying drawings illustrate in the form ofdiagrammatic flow plans two methods for applying the invention. InFigure 1, crude benzene hexachloride is charged to an extractor 10 whichmay comprise a closed, stirred vessel maintained at a suitabletemperature. Recycle solution or filtrate from the separation of gammaisomer is also charged to the extractor and the mixture is thus treatedfor about four hours. The extraction mixture is charged to a separatorprises largely alpha and beta benzene hexachloride together with minorproportions of delta benzene hexachloride and heptachlorocyclohexanewhich were not dissolved in the extraction step. The cake after washingwith fresh solvent is substantially free from gamma isomer. The washingsare segregated from the original filtrate and separated in a washsolvent still 12 into recovered wash solvent and residual benzenehexachloride both of which are recycled. The original filtrate ischarged to a crystallizer 13 which is maintained at a slightly lowertemperature than extractor The crystallizer may comprise a closed,stirred vessel provided with suitable means for temperature control, forexample, a jacket in which a liquid may be circulated. The contents ofthe crystallizer are thus cooled to a temperature slightly below that ofthe extraction step. Under these conditions, gamma isomer crystallizesand the solution remains supersaturated in alpha, beta and delta isomersof benzene hexachloride as well as heptachlorocyclohexane and any otherco-products. The mixture is charged to separator 14, suitably acentrifuge or filter, and separation is conducted at the crystallizationtemperature. The cake is washed with fresh solvent to obtain a puregamma cake. The washings are collected separately from the originalfiltrate and sent to wash solvent still 12. The filtrate, saturated atthe lower temperature with gamma isomer but supersaturated with respectto other isomers and co-products, is returned to extractor 10. At thehigher temperature maintained in the extractor the solution is saturatedwith co-products but not saturated with respect to gamma isomer.Extraction of fresh crude benzene hexachloride therefore results in theremoval of gamma isomer from the charge but no further quantities ofcoproducts are removed from the solid.

As illustrated in Figure 2, the liquor separated from the alpha, betacake before washing is collected in a surge tank having a four-hourcapacity, for example, and which is maintained at the extractiontemperature. A. batch crystallizer 13 of, say, two hours capacity ischarged from the surge tank 15 and the gamma benzene hexachloride iscrystallized by cooling. The liquor from the second separator 14 beforewashing the gamma cake is collected in a second surge tank .16 also offour hours capacity. The liquor is maintained therein at crystallizationtemperature. Recycle solution is removed continuously from surge tank16, warmed and charged to the continuous extractor. An advantage ofprocessing according to Figure 2 is that any tendency of delta benzenehexachloride to crystallize is avoided by maintaining it in surge tank15 at extraction temperature or slightly higher for a substantialholding period, e.g. one-half hour to 12 hours or more depending uponthe capacity of the processing system. Any remaining crystal nucleipassing through separator 11 are thus disintegrated. Delta isomer isless likely to separate at the lower temperature in crystallizer 13 andcontaminate the more readily crystallized gamma. The delta isomer ismore likely to be present in crystalline form in the surge tank 16,which is held at crystallization temperatures or slightly lower and inthe liquor recycled to the extractor where crystalline delta isdesirable to prevent extraction of delta from the charge.

Several critical conditions are to be observed in the operation of theprocess. It is important that a condition essentially of equilibrium isobtained between crystalline and dissolved phases of the components ofthe charge other than the gamma isomer. This is advantageouslyaccomplished by charging crude benzene hexachloride containing theisomers especially delta benzene hexachloride and heptachlorocyclohexaneat least partially in crystalline form. Crystallized deltabenzenehexachloride and heptachlorocyclohexane in crude benzene hexachloride donot dissolve in the extraction liquor. When such isomers are presentwholly in liquid form in the crude, they may dissolve and build updisadvantageously in the circulating solution. If the isomers arepresent in the crude charge at least partially in crystalline form,seeds or nuclei are provided on which the remainder or non-crystallineportion can crystallize to form an equilibrium solution. For thisreason, it is advantageous to use a charge of crude benzene hexachloridewhich is somewhat aged after its recovery from the process ofpreparation. Commonly only a fraction of the benzene charged to thechlorination process reacts and the crude product is obtained bydistilling off the excess benzene. The crude residue contains the deltaand hepta compounds in liquid form for some time. In order to use thematerial in the present process it may advantageously be aged until atleast part of these isomers have crystallized, which may require aperiod of several hours to several days but can be determined bymicroscopic analysis or by solubility determinations. Alternatively,nuclei and growing crystals may be maintained in the extraction vessel(which in effect functions as an equilibrium crystallizer) in a mannerinsuring that the solution leaving the vessel is essentially atequilibrium, i.e. just saturated with all components in the feed. Underthis condition, the charge need not be in the crystalline state but maybe in liquid form.

It is essential that the solution leaving the extraction vessel is inequilibrium at the extracting temperature with crystalline delta benzenehexachloride and heptachlorocyclohexane. On cooling to a lowertemperature to crystallize the gamma benzene hexachloride, the delta andhepta components then remain completely in supersaturated solution. Inaddition, the gamma isomer must not supersaturate in the solution underthe conditions of crystallization to an extent interfering with itsseparation as a solid. To accelerate crystallization, the liquor may beinoculated with a small portion of pure gamma crystals. The filtratefrom the crystallization is saturated with respect to gamma at thecrystallization temperature but unsaturated with respect to gamma at thehigher extraction temperature. Holding time is provided in each stage topermit the desired conditions for practical operation to be attained,i.e. essentially complete equilibrium in the first stage and incompleteor non-equilibrium conditions in the second stage. Usually a period ofan hour or more is necessary dependent upon temperature and contactconditions so that it is advantageous for continuous processing toprovide special holding stages in conjunction with the extraction,crystallization and separation equipment. Thus unit capacity isincreased and flexibility is provided in the event of operating upsetsor variations.

In order that delta and hepta may not crystallize in the crystallizationstep but remain in supersaturated solution, it is necessary that thetemperature differential between the two principal steps be small, e.g.about 5 2() C. For example, an extraction temperature of about 35 C. anda crystallization temperature of about 25 C. have been foundparticularly advantageous. Temperatures up to about 55 C. may be used inthe extraction step but at higher temperatures the delta isomer may notbe present to a suflicient degree in crystalline form and will tend todissolve and accumulate in the circulating liquor. For this reasontemperatures of about 25 50 C. are preferred for the extraction step. Inorder to insure the non-crystallization of delta and hepta in thecrystallization step, the temperature of the latter operation should notbe more than about 15 below the temperature of extraction step; Forexample, if the extraction is carried out'at 40 C.,'the temperature ofthe crystallization step preferably should not be below 25 C.

The chlorinated solvents, particularly perchloroethylene are preferredsince the solubility of delta benzene hexachloride therein is lower thanthe solubility of gamma. This reduces the bulk of delta in thecirculating liquor and reduces the possibility of crystallization ofdelta with the gamma isomer. Solvents in which the delta isomer is moresoluble than gamma are slightly less advantageous, but are satisfactoryfor use as long as they are capable of maintaining delta insupersaturated solution at the lower temperature of crystallization.Other solvents which may be used include benzene, trichlorobenzcne,beta, beta- Example I A crude benzene hexachloride containing deltabenzene hexachloride and heptachlorocyclohexane partially in crystallinecondition and having a composition of 73.6% of alpha and beta benzenehexachlorides, 13.7% of gamma and 12.7% of delta benzene hexachlorideand heptachlorocyclohexane was stirred with an equal weight ofperchloroethy-lene at 35 C. for four hours. The mixture was filtered at35 C. and the cake was washed with a small amount of fresh solvent. Thewashings were collected separately from the original filtrate. Thelatter was subsequently cooled to 25 C. and stirred for two hours. Themixture was filtered at 25 C. and the cake was washed with a smallquantity of fresh solvent. The washings were kept separate from thefirst filtrate which was warmed to 35 C. and used for the extraction ofadditional crude benzene hexachloride.

After six cycles of operation as described in the preced' ing paragraph,a solution was obtained which comprised 6.1% of alpha and beta isomers,14.4% of gamma, 19.2% of delta benzene hexachloride andheptachlorocyclohexane and 60.3% of perchloroethylene. A crude benzenehexachloride containing 75% of alpha and beta isomers, 11.5% of gammaand 13.5% of delta benzene hexachloride and heptachlorocyclohexane wasstirred for 4 hours at 35 C. with about times its weight ofthe solutionresulting from the above described cyclic,

operation. The mixture was then filtered at 35 C. to obtain a filtratewhich was saturated at 35 C. with respect to all of the isomers. Theundissolved solid contained 84.2% of alpha and beta isomers, 0.9%- ofgamma, 14.9% of delta benzene hexachloride and heptachlorocyclohexane.Adhering mother liquor amounted to 12.2% of the weight of undissolvedsolid. The filtrate Was cooled to 25 C. and maintained at thattemperature with agitation for two hours. The crystals of gamma isomerwere removed by filtration and amounted to 89.3% of gamma isomer chargedin the crude benzene hexachloride. The product was 98% gamma isomer.

On a larger scale and particularly using a higher ratio of recyclesolution to crude charge, the gamma content of the undissolved cake issubstantially all extracted. Gamma in the mother liquor is eventuallycompletely recovered as the solution is recycled between the extractionand crystallization steps.

Example I] The crude benzene hexachloride used in this example amountedto 124 parts by weight containing 75.5% of alpha and beta isomers, 14%of gamma and 10.5% of delta benzene hexachloride andheptachlorocyclohexane. In this material the delta benzene hexachlorideand heptachlorocyclohexane were present as crystalline materials. Thefinely divided solid was stirred for eight hours at 35 C. with 478 partsby weight of a solution containing 8% of alpha and beta isomers, 18.2%of gamma isomer, 30.1% of delta and hepta and 43.7% of carbontetrachloride. The undissolved residue was separated by filtration andwashed to remove adhering mother liquor. It then had a composition of86.3% alpha and beta isomers, 1.8% of gamma and 11.9% of delta benzenehexachloride and heptachlorocyclohexane. The filtrate from this cake wasstirred-at 25 C. for two hours and the resulting gamma benzenehexachloride crystals were removed by filtration. The filtrate wasrecycled to extract fresh crude benzene hexachloride. The filter cakeswere washed with fresh solvent,'the washings were distilled to recoverthe solvent and the residual material was recycled for use in furtherextraction. The recovery of the gamma isomer amounted to 88.2% of 94.5%purity.

Example 111 The procedure of the preceding example was repeated usingbenzene as solvent with substantially the same results.

Example IV Mixed isomeric trichlorobenzenes were utilized as solventaccording to the procedure described in the preceding examples withequally satisfactory results.

We claim:

1. A continuous process for the separation of gamma benzene hexachloridefrom a charge of crude benzene hexachloride consisting essentially ofthe alapha, beta, gamma and delta isomers and heptachlorocyclohexane bymeans of solvent extraction with a solvent capable of maintaining thedelta isomer and heptachlorocyclohexane in supersaturated solution andwhich is characterized by cyclic operation in which solution iscirculated in a closed cycle between a warm extraction stage and a coolcrystallization stage, the improvement which consists in aging a chargeof crude benzene hexachloride until at least part of the delta isomerand atleast part of the heptachlorocyclohexane are in crystalline form,contacting the aged crude benzene hexachloride charge in the extractionstage with solution recirculated from the crystallization stage andwarmed to about 25-50 C. until the solution is saturated in gammabenzene hexachloride, the solution leaving the extraction stagecharacterized by being substantially in equilibrium with the non-gammacomponents of the charge in the extraction stage, separating theundissolved material from the extracting solution, charging the solutionto the crystallization stage, crystallizing the gamma benzenehexachloride from the solution by cooling the solution to within therange of about 15 C. below the temperature in the extraction stage,separating crystals of gamma benzene hexachloride from the cooledsolution, warming the solution to the extraction temperature andrecirculating the resulting warmed solution saturated with the non-gammacomponents to the extraction stage for extraction of a fresh charge ofaged crude benzene hexachloride in which the delta isomer and theheptachlorocyclohexane are at least partially in crystalline form.

2. The process of claim 1 in which a chlorinated hydrocarbon solvent isemployed as the extracting and crystallizing medium. 1

3. The process of claim 2 where the chlorinated hydrocarbon solvent isperchlorethylene and the temperature employed in the extraction stage isabout 35 C. and the temperature employed in the crystallization stage isabout 25 C.

4. The process of claim 1 where the solution from the extraction stageis passed to a holding zone maintained at the extraction temperaturebefore being charged to the crystallization stage and the cooledsolution from the crystallization stage is passed to another holdingzone Where it is continuously withdrawn, warmed to the extractiontemperature and recirculated to the extraction stage.

References Cited in the file of this patent UNITED STATES PATENTS2,438,900 Cooke et a1 Apr. 6, 1948 2,574,165 Bender etal Nov. 6, 19512,708,681 Vossen May 17, 1955 2,760,995 Cragg et al. Aug. 28, 1956FOREIGN PATENTS 491,132 Belgium Mar. 16, 1950 680,955 Great Britain Oct.15, 1952 1,024,402 France Jan. 10, 1953

1.A CONTINOUS PROCESS FOR THE SEPARATION OF GAMMA BENZENE HEXACHLORIDEFROM A CHARGE OF CRUDE BENZENE HEXCHLORIDE CONSISTING ESSENTIALLY OF THEALPHA, BETA GAMMA AND DELTA ISOMERS AND HEPTACHLOROCYCLOHEXANE BY MEANSOF SOLVENT EXTRACTION WITH A SOLVENT CAPABLE OF MAINTAINIGN THE DELTAISOMER AND HEPTCHLOROCYCLOHEXANE IN SUPERSATURATEDF SOLUTION AND WHICHIS CHARACTERIZED BY CYCLIC OPERATION IN WHICH SOLUTION IS CIRCULATED INA CLOSED CYCLE BETWEEN A WARM EXTRACTION STAGE AND A COOLCRYSTALLIZATION STAGE, THE IMPROVEMENT WHICH CONSISTS IN AGING A CHARGEOF CRUDE BENZENE HEXACHLORIDE UNTIL AT LEAST PART OF THE DELTA ISOMERAND AT LEAST PART UNTIL AT LEAST PART OF THE DELTA ISOMER AND AT LEASTPART CONTACTING THE AGED CRUDE BENZENE HEXACHLORIDE CHARGE IN THEEXTRACTION STAGE WITH SOLUTION RECIRCULATED FROM THE CRYSTALLIZATIONSTAGE AND WARM TO ABOUT 25-50*C. UNTIL THE SOLUTION IS SATURATED INGAMMA BENZENE HEXACHLORIDE, THE SOLUTION LEAVING THE EXTRACTION STAGECHARACTERIZED BY BEING SUBSTANTIALLY IN EQUILIBRIUM WITH THE NON-GAMMACOMPONENTS OF THE CHARGE IN THE EXTRACTION STAGE, SEPARATING THEUNDISSOLVED MATERIAL FROM THE EXTRACTING SOLUTION, CHARGING THE SOLUTIONTO THE CRYSTALLIZATION STAGE, CRYSTALLIZING THE GAMMA BENZENEHEXACHORIDE FROM THER SOLUTION BY COOLING THE SOLUTION TO WITHIN THERANGE OF ABOUT 15* C. BELOW THE TEMPERATURE IN THE EXTRACTION STAGE,SEPARATING CRYSTALS OF GAMMA BENZENE HEXACHLORIDE FROM THE COOLEDSOLUTION, WARMING THE SOLUTION TO THE EXTRACTION TEMPERATURE ANDRECIRCULATING THE RESULTING WARMED SOLUTION SATURATED WITH THE NON-GAMMACOMPONENTS TO THE EXTRACTION STAGE FOR EXTRACTION OF A FRESH CHARGE OFAGED CRUDE BENZENE HEXACHLORIDE IN WHICH THE DELTA ISOMER AND THEHEPTACHLOROCYCLOHEXANE ARE AT LEAST PARTIALLY IN CRYSTALLINE FORM.